MDRD Equations for Estimation of GFR in Renal Transplant
After renal transplantation monitoring and detection of slight-to-moderate changes in GFR is a prerequisite for an optimal patient management. Recently, several equations to estimate GFR were developed and verified in the MDRD study cohort. However, little is known about the application of the MDRD formulas in the setting of renal transplantation.

We prospectively conducted a study of the GFR estimates of the Cockcroft and Gault (C&G), MDRD6-, MDRD7 and the abbreviated MDRD (aMDRD) with the true GFR as measured by Tc-DTPA clearance in 95 consecutive patients 6.5, 5.3—7.7 years (mean, 95% CI) after renal transplantation.

On average the DTPA clearance was 37.4, 34.440.4 mL/min/1.73m, which differed significantly from estimates of GFR by C&G (52.6, 48.356.9 mL/min/1.73m), MDRD7 (44.8, 40.7–49.0 mL/min/1.73m), MDRD6 (43.8, 39.947.7 mL/min/1.73m) and aMDRD (46.6, 42.450.9 mL/min/1.73m). Bias was lowest for MDRD6 (6.4 mL/min/1.73m) and highest for C&G (15.2 mL/min/1.73m). Precision was similar for MDRD7 and aMDRD (10.6 and 11.1 mL/min/1.73m) but significantly better for MDRD6 (8.6 mL/min/1.73m; p < 0.035). Accuracy within 50% of real GFR was 55.8% for C&G, 83.2% for aMDRD, 87.4% for MDRD7 and 90.5% for MDRD6.

MDRD equations perform significantly better than the commonly used C&G formula. Moreover, the MDRD6 equation provides the best diagnostic performance, and should therefore be preferred in renal

In patients after kidney transplantation monitoring of graft function requires accurate methods to detect even slight deteriorations of graft function. As proposed by the DOQI guidelines, serum creatinine alone should not be used to assess kidney function. Therefore, calculating GFR from creatinine-based methods is recommended. Unfortunately, the most commonly used Cockroft and Gault formula (C&G) as well as the standard creatinine clearance have been reported to overestimate real GFR in patients after renal transplantation by 30–38%, respectively. As a consequence, alternative and more precise equations to estimate GFR are warranted.

Recently, the so called MDRD formulas for GFR estimation were derived by computer modeling from the 1628 patients of the modification of diet in renal disease (MDRD) study population. The equations include parameters as sex, age, race, serum levels of albumin, creatinine, urea nitrogen and urinary urea nitrogen. The most precise MDRD formulas (MDRD6, MDRD7) are based on six different variables. A simplified equation based on four parameters (abbreviated MDRD = aMDRD) was developed later showing similar performance as the MDRD7 equation. Thus, due to its simplicity the aMDRD equation seems appropriate for routine use. Although particular MDRD formulas have been applied to renal transplant recipients studies comparing the results of different MDRD formulas with the true GFR as measured by a reference method are rare. The aim of the present study was to evaluate the diagnostic precision of the C&G formula, the MDRD6, the MDRD7 equations, as well as the aMDRD formula in an unselected consecutive cohort of renal transplant recipients that had their GFR determined by a gold standard method.